1. Field of the Invention
The present invention relates to an electronic circuit on which an integrated circuit and a decoupling capacitor for stably operating the integrated circuit are mounted on a multilayer circuit board, and particularly relates to an electronic circuit in which an impedance value of the decoupling capacitor in a wide frequency band is reduced.
2. Description of Related Art
Various integrated circuits (such as ICs and LSIs) including various functions of a microcomputer, a logic circuit or the like are used as key components of various electronic and information devices. Since an integrated circuit malfunctions unless a current is instantaneously supplied thereto in an operating frequency band, a decoupling capacitor connected between an operation power-supply potential and a ground of the integrated circuit is disposed around the integrated circuit.
In recent years, the operating frequency band of integrated circuits has been widened, but the frequency band that a single decoupling capacitor having a fixed capacitance value is able to can compensate is limited. Therefore, in order to compensate the operation of a single integrated circuit in a wideband operating frequency, multiple decoupling capacitors are necessary. In addition, in recent years, the supply current required by the integrated circuits has been steadily increasing, and the higher the load on the integrated circuit, the larger the number of required decoupling capacitors.
In order to dispose a large number of decoupling capacitors to cope with an increase in the number of decoupling capacitors required for a single integrated circuit, and also in order to cope with an increase in the number of pins due to the increased functions of integrated circuits themselves, a multilayer circuit board formed by laminating a plurality of layers on a single substrate is used as a circuit board for mounting an integrated circuit.
A multilayer circuit board is formed by laminating a plurality of insulating hard substrates, on each of which a conductor wiring pattern is formed on one or both surfaces, and integrating the insulating hard substrates by heat pressing. By filling the inside of via holes formed by penetrating the insulating hard substrates with a conductive material, electrical connection is established between predetermined terminals on different layers. By combining this inter-layer connection established by the via holes and connection by wiring patterns disposed on the surface of the substrates, numerous electrical wirings can be disposed in a small area. Such a multilayer circuit board is disclosed in, for example, JP 2001-217550A, and JP 2007-305642A.
In an electronic circuit that uses a multilayer circuit board and on which an integrated circuit is mounted, the integrated circuit formed on one of the main surfaces of the multilayer circuit board is connected to a decoupling capacitor disposed on the same main surface or the opposite main surface through wiring patterns formed on the layers and via holes connecting the layers.
In the case where an integrated circuit and a decoupling capacitor are mounted on a multilayer circuit board, in order to set the effective capacitance value of the decoupling capacitor to a desirable value, it is required to suppress a resistance component of the wiring patterns and via holes of the multilayer circuit board which are interposed between the terminals of the decoupling capacitor and the integrated circuit as much as possible. For this purpose, the decoupling capacitor is disposed in a position that is physically close to the integrated circuit, thereby reducing the length of the current flow path. Also, the thickness of the wiring patterns on the layers of the multilayer circuit board is increased, the area of an isolated pattern called a land formed by connecting portions having the same potential is increased, or as large a number of via holes as possible are used between a pair of terminals for establishing electrical connection between substrates, thereby reducing the electrical resistance value in connecting wiring portions.
However, in order to cope with high current driving that has accompanied the recent improved performance of integrated circuits, at present a sufficient level has not yet reached in terms of shortening the current flow path or reducing resistance.